This invention relates to heat transfer surfaces for nucleate boiling and improved means for producing such surfaces. For an extensive discussion of nucleate boiling and prior art patents related thereto, reference may be made to the disclosure of Janowski et al co-pending U.S. Application Ser. No. 769,623, filed Feb. 16, 1977, now U.S. Pat. No. 4,129,181 and assigned to a common assignee, the subject matter of which is incorporated by reference herein. The aforementioned Janowski et al application discloses the concept of applying a porous reticulated foam layer to the surface of a tube or other heat transfer surface and then coating the foam layer and tube with a metal layer which will surround the internal skeleton of foam and have the same reticulated shape. Although the Janowski et al application teaches that the internal reticulated foam structure may be left intact or pyrolyzed to produce additional nucleation sites, it has been found that the initial good boiling performance of a tube covered with metallized foam having a pore size of about 45 pores per inch which has been fully pyrolyzed can deteriorate if boiling is extended over a period of time, such as several days. Since the tube surface cannot be studied during boiling, it is only conjecture that some of the initially active boiling sites which are presumed to exist at the ends and open portions of the hollow metal strands which remain after pyrolysis are "flooded out" by continued boiling. For example, it is conceivable that some of the vapor bubbles which are ordinarily trapped at the initially active boiling sites are washed away by the liquid, thus reducing the number of active boiling sites and the efficiency of boiling. Where the foam has a smaller pore size, such as 75 pores per inch, the boiling performance of a pyrolyzed tube does not seem to deteriorate in time since the diameter of the hollow strands formed from 75 pore per inch reticulated foam are smaller than the strands formed from 45 pore per inch foam.